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Molt in Birds Inhabiting a Human-Dominated Habitat

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Molt is one of the biological processes in the life of birds that requires high energy. Therefore, it usually occurs when food is abundant. However, molt and breeding overlap have been recorded in the tropics. There are very few studies on bird molting patterns in Indonesia. This study aimed at describing molt in birds that inhabit a human-dominated habitat in Bogor Agricultural University Campus in Bogor, West Java. Molt of primary feathers of adult birds were checked during bird monitoring using mist nets from August 2010 to December 2013. Occurrence of brood patch as indicator of breeding stage was also recorded. Molt data were obtained from 230 adult birds from 29 species. Molts occurred from February to December, with most birds having active molts in July and October. Breeding occurred in March, April, July, and October, with the peak of breeding occurring in March. Molt and breeding overlap were identified only in three species, i.e. Eurasian Tree Sparrow (Passer montanus), Horsfield's Babbler (Malacocincla sepiarium), and Scarlet-headed Flowerpecker (Dicaeum trochileum). This study suggests that resources in the study site are available for conservation of bird community in human-dominated habitat. However, further research is needed to assess food availability and bird breeding success.
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Original Research Article
Molt in Birds Inhabiting a Human-Dominated Habitat
Yeni Aryati Mulyani,
1*
Fransisca Noni Tirtaningtyas,
1
Nanang Khairul Hadi,
2
Lina Kristina Dewi,
3
Aronika Kaban
1
1
Department of Forest Resources Conservation and Ecotourism, Faculty of Forestry, Bogor Agricultural University, Bogor, Indonesia.
2
Study Program Natural Resources and Environmental Management, Graduate School, Bogor Agricultural University, Bogor, Indonesia.
3
Jalan Cempaka, Perumahan Dosen, Bogor, Indonesia.
article info
Article history:
Received 31 August 2015
Received in revised form
28 August 2016
Accepted 1 November 2017
Available online 11 December 2017
KEYWORDS:
birds,
molt,
molt-breeding overlap
abstract
Molt is one of the biological processes in the life of birds that requires high energy. Therefore, it usually
occurs when food is abundant. However, molt and breeding overlap have been recorded in the tropics.
There are very few studies on bird molting patterns in Indonesia. This study aimed at describing molt in
birds that inhabit a human-dominated habitat in Bogor Agricultural University Campus in Bogor, West
Java. Molt of primary feathers of adult birds were checked during bird monitoring using mist nets from
August 2010 to December 2013. Occurrence of brood patch as indicator of breeding stage was also
recorded. Molt data were obtained from 230 adult birds from 29 species. Molts occurred from February
to December, with most birds having active molts in July and October. Breeding occurred in March, April,
July, and October, with the peak of breeding occurring in March. Molt and breeding overlap were
identied only in three species, i.e. Eurasian Tree Sparrow (Passer montanus), Horseld's Babbler (Mal-
acocincla sepiarium), and Scarlet-headed Flowerpecker (Dicaeum trochileum). This study suggests that
resources in the study site are available for conservation of bird community in human-dominated
habitat. However, further research is needed to assess food availability and bird breeding success.
Copyright ©2017 Institut Pertanian Bogor. Production and hosting by Elsevier B.V. This is an open access
article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
1. Introduction
Birds need to change their feathers once in a while. There are
times in the life cycle of birds that its plumages get worn and need
replacement. Young birds also changed their plumage when they
grew up. This process is known as molting. Molt is simply the
replacement of feather. It is also one of the most fundamental
processes of any bird's life cycle. Feathers are not permanent
structures and need to be replaced. Therefore, molting involves
detachment of old feathers and growth of new feathers. This pro-
cess makes birds need high energy during molting. Previous studies
(Murphy &King 1982) stated that birds cope with the situation by
adjusting their food consumed or using their endogenous reserve
or alteration in the timing of activities that require high energy such
as breeding. Therefore, most birds usually do not coincide their
timing of molt with their timing of breeding; although there are
records of molt and breeding overlaps in the tropical birds such as
reported by Miller (1961).
The reasons behind the high occurrence of molt breeding
overlap may lie in the combined effect of reduced seasonality of
tropical environments, competition, and the increased risk of nest
predation in these areas (Cody 1966; Ricklefs 1969). In temperate
species, timing of breeding and molt is generally constrained by
food availability and periods of thermal stress such that both ac-
tivities must occur during the summer months. In contrast, the
reduced seasonality in tropical climates permits a longer breeding
season (Ricklefs 1969). Despite this, competition for food (Karr &
Brawn 1990; Poulin et al. 1992; Recher 1990), low reproductive
success (through high levels of nest predation) (Scheuerlein &
Gwinner 2002; Weidinger 2002), and extended parental care
(Russell et al. 2004; Schaefer et al. 2004) may all combine to make
the length of time required for the successful production of each
offspring much greater than for temperate areas. It has therefore
been argued that molt may be just as time constrained in tropical
areas as temperate areas.
There are very few studies on bird molt in Indonesia (Novarino
2008). Regarding energy requirement for molting and breeding
birds, loss of natural habitats because of conversion to other land
usesdwhich is highly increasingdmight inuence the pattern of
molt and breeding. Human-modied habitats might increase food
*Corresponding author.
E-mail addresses: yenimulyani@ipb.ac.id,yamulyani@gmail.com (Y.A. Mulyani).
Peer review under responsibility of Institut Pertanian Bogor.
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Contents lists available at ScienceDirect
HAYATI Journal of Biosciences
journal homepage: http://www.journals.elsevier.com/
hayati-journal-of-biosciences
https://doi.org/10.1016/j.hjb.2017.11.004
1978-3019/Copyright ©2017 Institut Pertanian Bogor. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://
creativecommons.org/licenses/by-nc-nd/4.0/).
HAYATI Journal of Biosciences 24 (2017) 195e200
availability for some bird species through the planting of fruit-
bearing trees or owering trees and on the other hand might
reduce some resources for other bird species. Reduced food in
disturbed habitat might affect molting in birds (Freed &Cann
2012).
Lack of molt studies in Indonesia might be due to limitation in
equipment and skill in capturing birds for research. In 2010, Indo-
nesian Bird Banding Scheme (IBBS) was established by The Indo-
nesian Institute of Sciences (LIPI), and one of its goals is to promote
bird banding as one of the standard methods for bird monitoring in
Indonesia. To achieve the goal, trainings have been conducted for
interested individuals and groups. This study is a part of a regular
bird monitoring program and training using mist nets by a group of
bird banding enthusiasts in Bogor Agricultural University, the
Cikabayan Bird Banding Club, in which the authors are members.
2. Materials and Methods
Data were collected in Bogor Agricultural University Darmaga
Campus from August 2010 to December 2013. The area is located
in the District of Bogor, West Java Province, Indonesia
(6
o
33'29.9''Se106
o
43'25.4''E). The 267 ha area is consisted of
several habitat types, including buildings, parks, lakes, arboretum,
garden, man-made forest, and agricultural land. The area is known
to have relatively high bird diversity, with no less than 85 species
recorded in the area (HIMAKOVA 2012). Situated in the tropics, the
area has a mean temperature of 26
C and high relative humidity
(70%e90%) as well as high annual rainfall (3000e5000 mm per
year).
Molt data were collected by capturing birds using mist nets.
Six to eight mist nets were set up for 2 days every 1e3 months
from August 2010 to December 2013 in 10 sampling sites, which
comprise different habitat types (home garden, mixed tree plan-
tation, and bushes) (Figure 1). Each site did not receive similar
mist netting effort because of logistic problems; the most fre-
quented were Cikabayan site (mixed agricultural farm and plan-
ted woodlot). Mist nets were opened from 6.00 to 17.00 hours. To
prevent risk of injury for birds, nets were closed during rain and
very hot weather. Nets were checked every hour, and sometimes,
when predators were suspected or depending on weather con-
dition, nets were checked every 30 minutes. Any bird caught in
the mist net would soon be released, put into bird bag, and
brought to the banding station to be identied, aged, sexed,
banded using IBBS numbered ring, measured, and checked for
primary feather molt. The numbered ring was not applied to swift
and swiets because no rings for the species are available from
IBBS. Occurrence (the presence and/or the absence) of brood
patch, an indication of breeding activity, was also noted. Birds
captured were categorized as adults, immature, or juveniles by
plumage and bare parts coloration. Age classication and sex
determination followed Lowe (1989),MacKinnon et al. (2010),and
Robson (2000).
Each primary feather molt was scored 0, 1, 2, 3, or 5, following
guidelines from the study by Ginn and Melville (1983). Total molt
score is calculated from left wing only; therefore, it ranged between
0 and 50. A bird with a total molt score of 0 is categorized as having
no molting activity, whereas a bird with a total molt score of 50 is
categorized as having new feathers (has nished molting).
Figure 1. Location of sample sites (red dot).
Y.A. Mulyani, et al196
Therefore, a bird with active molt had a total molt score between 1
and 49. Molt analysis was done only by using data from adult birds.
There were several cases when the measurements were not done
for all birds. The reasons for this were as follows: (1) the bird
escaped during process or (2) the bird was released to reduce the
stress of the bird, especially when it was badly entangled in the net.
Analysis of molt pattern was only done for birds with at least 10
individuals. Data from 2010 to 2013 were lumped to analyze the
timing of molt.
3. Results
A total of 497 individuals from 33 species were captured during
the study, including 33 retraps (captured more than once). There
was a variation in the number of captured birds based on age
classes (Figure 2), with Eurasian Tree Sparrow (Passer montanus)
being the largest number followed by Sooty-headed Bulbul (Pyc-
nonotus aurigaster), Scarlet-headed Flowerpecker (Dicaeum trochi-
leum), and Scaly-breasted Munia (Lonchura punctulata). Two
hundred thirty individuals of 29 species were categorized as adult.
Looking at the molt scores of those adult birds, it showed that molt
occurred from February to December, with most birds having active
molt in July and November. Breeding, as indicated by the occur-
rence of brood patch, occurred in March, April, July, and October,
with the peak of breeding occurred in March (Figure 3).
Eight species had more than 10 individuals caught, and it
showed that there are differences in the timing of molt among
species (Table). However, the data are fragmented because species
captured were not consistent every month. For example, the
highest number of captures was Eurasian Tree Sparrow (Passer
montanus), but data were only available for March, April, and
October, where many of the birds showed active molt. New feathers
were found in March and October. Scatter plots of molt score of ve
sampled species showed that most birds presumably started
molting between March and June (Figures 4e8), although the
length of molt period varied.
Birds that showed brood patch and molting at the same time are
Eurasian Tree Sparrow (Passer montanus)(n¼10), Horseld's
Babbler (Malacocincla sepiarium)(n¼1), and Scarlet-headed
Flowerpecker (Dicaeum trochileum)(n¼1). Molt and breeding
overlap in Eurasian Tree Sparrow occurred in March and October,
whereas in Horseld's Babbler, it occurred in March, and in Scarlet-
headed Flowerpecker, it occurred in July.
4. Discussion
Molting may vary according to resource availability and species
characteristics. In Borneo, Fogden(1972)found that molting occurred
soon after breeding season, and birds nished molting in November,
the period when food abundance (insects) was decreased. Larger
Figure 2. Variation in the number of birds captured based on age classes.
Figure 3. Variation in the number of molting and breeding birds.
Molt in birds 197
birds also tend to have a longer period to complete their molting
session (Ginn &Melville 1983). Novarino (2008) found that in Sipi-
sang, West Sumatra, most birds undergone molting almost all year
round with the peak occurring from July to September. This peak
coincided with the end of breeding season. He suggested that this
relates to nutrition requirement and food availability.
Compared with other species in this study, Sooty-headed Bulbul
is a relatively large bird. This species feed on fruits and insects
(MacKinnon et al. 2010). Sooty-headed Bulbulis is a successful and
adaptable species found in open country with scattered bushes and
trees. Therefore, food might not be the limiting factor for molting of
this species in the study site. This also applies to Eurasian Tree
Table. Number of individuals with active molt (nper species 10 individuals; eindicated that no birds were captured)
Month Collocalia linchi
(n¼15)
Dicaeum trochileum
(n¼15)
Hirundo tahitica
(n¼15)
Orthotomus
sepium (n¼17)
Orthotomus
sutorius (n¼10)
Passer
montanus (n¼48)
Pellorneum
capistratum (n¼14)
Pycnontotus
aurigaster (n¼36)
January ee e e e e e e
February e0e20 ee 1
March 0 e100 10 2 1
April e1e02 0 1 3
May ee e e e 10 2
June 2 1 0 2 2 e13
July 0 2 e1ee e 2
August ee e e e e e e
September e0e20 e0e
October 2 1 0 1 e12 2 1
November 0 0 e10 ee 6
December 0 0 e1ee e 1
Figure 4. Scatter plot of molt score of Sooty-headed Bulbul (Pycnonotus aurigaster).
Figure 5. Scatter plot of molt score of Scarlet-headed Flowerpecker (Dicaeum trochileum).
Y.A. Mulyani, et al198
Figure 6. Scatter plot of molt score of Javan Tailorbird (Orthotomus sepium).
Figure 7. Scatter plot of molt score of Common Tailorbird (Orthotomus sutorius).
Figure 8. Scatterplot of molt score of Black-capped Babbler (Pellorneum capistratum).
Molt in birds 199
Sparrow, in which breeding and molting occurred. Eurasian Tree
Sparrow could consume a varied type of food, from grains to food
scraps, and they are locally abundant in town, villages, and rural
development (Strange 2001).
Although the data in this study are still limited, it suggest that
variation in habitat types provides resources for bird community in
the study site. However, further research is needed to assess food
availability and bird breeding success. Planting of fruit-bearing
trees in the housing area and experimental farm provided food for
this species, so it can fulll energy requirement for molt.
Conict of Interest Statement
There is no conict of interest.
Acknowledgements
The authors thank other members of Cikabayan Bird Banding
Club who have voluntarily helped in collecting data. They also
thank Dr Dewi M. Prawiradilaga from the Indonesian Institute of
Science (LIPI) who has been always supportive with our bird
banding activities, including lending us the equipment and bands.
They also thank their trainers from Australia Bird and Bat Banding
Scheme, especially Mr Alan Leishman, who also supported them
with some equipment.
References
Cody ML. 1966. A general theory of clutch size. Evolution 20:174e84.
Fogden MPL. 1972. The seasonality and population dynamics of equatorial forest
birds in Sarawak. Ibis 114:307e43.
Freed LA, Can RL. 2012. Increase of an introduced bird competitor in old-growth
forest associated with restoration. NeoBiota 13:43e60.
Ginn HB, Melville DS. 1983. Moult in Birds. BTO Guide 19. BTO, Tring.
HIMAKOVA. 2012. Buku Panduan Lapang Burung Kampus IPB Darmaga. IPB Pr,
Bogor (ID).
Karr JR, Brawn JD. 1990. Food resources of understorey birds in Central Panama:
quantication and effects on avian populations. Stud Avian Biol 13:58e64.
Lowe KW. 1989. The Australian Bird Bander's Manual. Australian Bird and Bat
Banding Schemes. Australian National Parks and Wildlife Service.
MacKinnon J, Phillips K, van Balen B. 2010. Burung-burung di Sumatera,
Jawa, Bali da n Kaliman tan. LIPI/Perhimpunan Pelestarian Burung Liar di
Indonesia, Indonesia.
Miller AH. 1961. Molt cycles in equatorial andean sparrows. Condor 63:143e61.
Murphy ME, King JR. 1982. Amino acid composition of the plumage of the White-
crowned Sparrow. Condor 844:351e438.
Novarino W. 2008. Dinamika Jangka Panjang Komunitas Burung Strata Bawah di
Sipisang, Sumatera Barat [Disertasi]. Sekolah Pascasarjana IPB.
Poulin B, Lefebvre G, McNeil R. 1992. Tropical avian phenology in relation to
abundance and exploitation of food resources. Ecology 73:2295e309.
Recher HF. 1990. Specialist or generalist: avian response to spatial and temporal
changes in resources. Stud Avian Biol 13:333e6.
Ricklefs RE. 1969. The nesting cycle of songbirds in tropical and temperate regions.
Living Bird 8:165e75.
Robson C. 2000. A Field Guide to the Birds of South-East Asia. New Holland Pub-
lisher Ltd, United Kingdom.
Russell EM, Yom-Tov Y, Geffen E. 2004. Extended parental care and delayed
dispersal: northern, tropical and southern passerines compared. Behav Ecol 15:
831e8.
Schaefer HC, Eshiamwata GW, Munyekenye FB, Bohning-Gaese K. 2004. Life-history
of two African Sylvia warblers: low annual fecundity and long post-edging
care. Ibis 146:427e37.
Scheuerlein A, Gwinner E. 2002. Is food availability a circannual zeitgeber in
tropical birds? A eld experiment on Stonechats in tropical Africa. J Biol
Rhythms 17: 171 e80.
Strange M. 2001. A Photographic Guide to the Birds of Indonesia. Periplus Edition,
Singapore.
Weidinger K. 2002. Interactive effects of concealment, parental behaviour and
predators on the survival of open passerine nests. J Anim Ecol 71:424e37.
Y.A. Mulyani, et al200
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A principal finding in a year-long study of an equatorial population of Andean Spar-rows (Zonotrichia capensis) in Colombsa was that each individual displays two breeding periods in one year (Miller, 1959). This is particularly clear in males in which there are two complete regressions and two full regrowths of the testis over a 12-month period, the 6-month norm for the completed cycle reflecting an innate cyclic tendency which is only partly coerced by the rainfall cycle. At least some individuals in full reproductive capacity and some actual nestings may be found in every month of the year. In north temperate and arctic passerine birds it has long been recognized that among the non-migratory species the single, complete, annual molt follows the nesting period, and it has often been thought that this molt was physiologically related to the reproduc-tive cycle, being an expression ' in part of the drastic changes in hormonal balance that inevitably occur in the regressive period of the hypothalamic-pituitary-gonad mechan-ism. Experimental results in recent years, particularly in respect to the prenuptial molt, have tended to show a partial independence of the physiologic control of molt and the gonadal cycle (see, for example, Miller, 1954: 18, and Selander, 1958:366). But in any event from the ecologic and adaptive standpoint it has become increasingly clear that molt and nesting are functions which compete for energy and food resources and that the two, by whatever stimulating and physiologic mechanisms, are neatly timed in vari-ous ways to avoid a simultaneous drain on the bird and ' its environment. These matters have been especially brought to notice and analyzed by Pitelka (1958). In the light of these several circumstances it was surprising to find in equatorial populations of Zorzotrichia cape&s that two complete "annual" molts occur each year and that there are no partial, prenuptial molts. Moreover both a linking and a degree of independence of the schedules of molts and breeding states were observed and these matters require detailed exploration for their various implications. The complete molt in equatorial passerines is no less taxing a process than in northern species, if, as often proves true, it is pursued almost as rapidly as in northern types. Pitelka (1958) has shown that in the Steller Jay (Cyanocitta stelleri) the dry weight of the plumage mass represents about 10 per cent of the total weight of the bird and the assumption of a similar relation in Andean Sparrows suggests the appreciable energy drain in producing the plumage over a two-month period in addition to other normal activities. METHODS The general setting for this work and the procedure in following the cycles of indi-viduals has been described in part in earlier papers (1958; 1959). Throughout I was aided in trapping birds and recording weather by Virginia D. Miller and our daughters, Barbara and Patricia. Acknowledgment also is gratefully made of support by a Guggen-heim fellowship and of aid by F. Carlos Lehmann V. of the Universidad de1 Valle, Colombia. The particular data on molt were derived in three ways. (1) The 160 banded indi-viduals trapped and marked in an area of about 4 acres, from February 10, 1958, to January 22, 1959, were retrapped as often as possible, and on almost all occasions they were examined for molt. Thus in the year a total of 720 capture and recapture records was made; multiple captures on a ssngle day are not included. (2) Color-marked birds identified as individuals and closely followed with binoculars at close range were recorded as in molt when they showed conspicuous breaks in plumage of the body, wing, and tail.
Article
The principle of allocation of time and energy is used to formulate a general theory to account for clutch size in birds. "Advantages" are figured as the axes of a three-dimensional graph, and phenotypes allocating their energy in particular ways as points in space forming a surface and enclosed solid. In the temperate zones most energy is used to increase the reproductive rate r. In the tropics the carrying capacity of the habitat is more important, resulting in a smaller clutch size. Different phenotypes will be more fit in different environments, as optimum allocation of energy differs. Previous theories of clutch size are discussed, and incorporated into this general theory. Increase of clutch size with latitude is analyzed, and accounted for by the theory. Predictions are made that all stable environments, the tropics, islands, coasts, will favor reduced clutches. Examples are quoted in which instability of conditions results in increased clutch size. The situation of predation-free species is examined, and it is predicted that the clutch size of such species will remain relatively unchanged with latitude changes. These predictions seem to be verified in all cases where data are available to test them.
Article
Summary 1. A simple model of relative effects of parental behaviour (parents present vs. absent) and nest concealment on probability of nest predation was evaluated by measuring survival of paired natural/artificial nests of four open nesting passerines over 3 years. 2. The ratio of rodent to corvid predation (i) decreased from yellowhammer (small eggs, ground/near ground nests) through blackcap (small, shrub) to song thrush and blackbird (medium sized, shrub/subcanopy); (ii) was highest in years when rodent abundance peaked - this effect was clear in yellowhammer, detectable in blackcap, but not found in thrushes. An inverse relationship was found between mean annual nest sur- vival and abundance of the major nest predator for each species. Predators differed between poorly (corvids) and well-concealed (rodents) nests in blackcap. 3. The effects on nest survival differed among species, including: positive effect of parental behaviour combined with neutral effect of concealment (thrushes); independ- ent positive effects of behaviour and concealment (yellowhammer); neutral effect of behaviour combined with positive effect of concealment (blackcap). These patterns are consistent with hypothesis that relatively larger species with conspicuous nests (thrushes) should either engage in more vigorous nest defence or their defence is more efficient, compared with smaller species with less conspicuous nests (blackcap). 4. The positive relationship between nest concealment and survival resulted either from an effect of nest site per se (yellowhammer) or from an effect of parental behaviour (blackcap) that changed from negative (nest disclosure) to positive (nest defence) between poorly and well-concealed nests, respectively. The view that lack of a within- species relationship between nest concealment and survival (thrushes) results from parental behaviour compensating for predation risk associated with poor nest conceal- ment was not supported. 5. This study demonstrated (i) multiple interactions among factors influencing the rate of nest predation, both between and within species; (ii) potential bias associated with drawing general conclusions from small-scale experiments.